Study of choked flows through a convergent nozzle

Abstract

When sonic nozzles of significantly smaller diameter are used as standard flow meters, the critical back pressure ratio is affected by the boundary layer at the nozzle throat. However, the effect of the boundary layer on choking criteria is still controversial. Then, the choking phenomenon of a convergent nozzle flow has been experimentally investigated using four convergent nozzles with the same diameter followed by a straight pipe of a variable length.As a result, it is shown that the critical back pressure ratio is smaller than that for the steady one-dimensional isentropic flow and decreases as the boundary layer thickness increases. Moreover, the main flow Mach number at the nozzle exit is supersonic when the back pressure ratio is equivalent to the choking condition, and the Mach number increases as the boundary layer thickness increases.

Study on the compressible viscous flows through a straight pipe

“…3 and 4) predicted with the code and experiment [4]. Static pressure measurement positions (x/D) are shown in Fig.…”

“…However, interestingly, it is observed that the flow Mach number exceeds unity near the exit of the straight pipe and hence the flow chokes not at the pipe exit but well upstream of it. In addition, the critical pressure ratio predicted from the experiment is less than the ideal value [4]. In the present effort a large number of simulations are done with different L/D ratios to understand such flows near the pipe exit.…”

“…Their results showed that the critical backpressure ratio is a function of the Reynolds number only, not dependent on the throat diameter, and has different behaviors for different nozzle shapes. Recently, Kubo et al [4] experimentally investigated the choking phenomenon in several straight pipes of variable lengths. It is shown that the critical backpressure ratio is smaller than that for the steady onedimensional theory and it decreases as the boundary layer thickness inside the straight pipe increases.…”

“…Motivated by these considerations, one of the simplest of these flows is examined during the present investigation, namely, flows through convergent nozzle fitted with several straight pipes. Kubo et al experimentally investigated choked flows through several constant area pipes [4], in which a sonic nozzle is fed from a large reservoir at a constant stagnation pressure (P 0 ) and temperature (T 0 ). The nozzle is fitted with a straight circular pipe of variable length and discharges into a chamber, whose pressure can be controlled by a vacuum pump.…”

Supersonic micro-jet of straight micro-tube exit

“…The thickness of the boundary layer formed on the channel wall is thin comparing with the channel size and the flow can be considered as one dimensional flow. However, Kubo et al (2010) measured the total pressure at the outlet plane for a tube of 15 mm in diameter. They reported that the flow velocity at the outlet plane of a straight millimeter sized channel exceeds the speed of sound.…”